Abstract. Inflammatory bowel disease, enterocolitis, colorectal cancer, Celiac sprue, and radiation injury are associated with damage to the intestinal epithelial barrier. The multifactorial nature of these pathologies, and the lack of targeted therapies for their treatment, underscores the need to define the mechanisms regulating intestinal epithelial barrier integrity. Chemokines are ubiquitous immune mediators that direct leukocyte trafficking. Chemokines are upregulated in human gastrointestinal disorders and are thought to contribute to defects in barrier permeability and to the exacerbation of disease. CXCR4 and its ligand CXCL12 form a homeostatic chemokine-chemokine receptor pair that is essential for constitutive immune responses. CCR6 and its ligands CCL20 and human betadefensin- 2 (HBD2) are inducibly expressed effectors of innate and adaptive immune responses. Work from the previously supported award indicates that CXCR4 and CCR6 are potent immune regulators of epithelial migration. The central hypothesis is that chemokine receptors control cell-cell and cellsubstrate adhesion components through specific intracellular signaling pathways. The objective is to define the integrated roles for CXCR4 and CCR6 as key regulators of restitution, the rapid enterocyte migration response critical for re-epithelialization of the mucosal barrier. Studies in Aim 1 will employ human model epithelial cells to test the hypothesis that chemokine-induced mobilization of intracellular calcium activates key downstream effectors to stimulate wound closure through reorganization actin cytoskeleton. In Aim 2, we will test the hypothesis that chemokine receptors coordinate tight interactions between neighboring epithelial cells and the underlying matrix through integrin and cadherin activation and localization. In Aim 3, we will test the hypothesis that targeted deletion of CXCR4 and CXCL12 in the cells of the intestinal epithelium impairs barrier integrity, mucosal re-epithelialization, and mucosal immune responsiveness in vivo. These studies will be the first to detail the mechanisms linking chemokine receptor signaling to the integrity and stability of the mucosal epithelium. Importantly, our results suggest a paradigm shift regarding a role for chemokines that goes beyond facilitating the trafficking of immune cells to the mucosa. Our work supports the model that chemokines also mediate key regulatory and signal transduction functions in rebuilding the injured epithelium. This application sets the stage for the rational design of therapeutic strategies to facilitate the healing of damaged tissues.